Amphibious vehicle speed change transmission arrangement

ABSTRACT

A power train configuration for an amphibious vehicle especially well suited for sit-astride applications. A prime mover drives a marine propulsion unit and/or at least one road wheel wherein the such road wheel is driven through a speed-change transmission. The speed-transmission is positioned above or below the axis of the prime mover&#39;s output shaft and preferably such that its input and output shafts are aligned at an angle of up to 90 degrees relative to the vehicle&#39;s longitudinal and lateral axes and/or the axis of the prime mover&#39;s output shaft.

CROSS-REFERENCES TO RELATED APPLICATIONS

This application claims priority from Great Britain Application SerialNo. 0422954.8, filed Oct. 15, 2004.

BACKGROUND OF THE INVENTION

The present invention relates to an amphibious vehicle capable ofpowered travel on land and water. The present invention relates inparticular, but not exclusively, to an amphibious vehicle in which auser sits astride the vehicle in the manner of a motorcycle, jet ski,quad bike, or the like.

Amphibious vehicles capable of powered travel on both land and water areknown. In a typical arrangement, a prime mover (such as an engine orelectric motor) is arranged to provide drive to a marine propulsion unitto propel the vehicle on water and to provide drive to one or more roadwheels for travel on land.

Because of the need to drive a marine propulsion unit and at least oneroad wheel, the power train of an amphibious vehicle is often morecomplex than that of a conventional road going vehicle or marine onlycraft. This can give rise to difficulties in designing a power train tobe accommodated in the limited available space, whilst also ensuringthat the weight distribution is satisfactory for both land and marineusage. This problem is particularly acute for smaller “sit-astride” typeamphibious vehicles that are similar in form to motorcycles, jet skis,or quad bikes. Such vehicles tend to have narrower, taller bodywork thatmakes it difficult to accommodate a conventional amphibious vehiclepower train.

There is a need, therefore, for an amphibious vehicle having an improvedor alternative power train layout that can be more easily accommodatedin a smaller or narrower space, particularly for a sit-astride typeamphibious vehicle.

SUMMARY OF THE INVENTION

According to an aspect of the present invention, there is provided anamphibious vehicle having a prime mover that drives a marine propulsionunit and/or at least one road wheel wherein the such road wheel isdriven through a speed-change transmission. The speed-transmission ispositioned above or below the axis of the prime mover's output shaft andpreferably such that its input and output shafts are aligned at an angleof up to 90 degrees relative to the vehicle's longitudinal and lateralaxes and/or the axis of the prime mover's output shaft.

It is a particular advantage of the present invention that thetransmission can be positioned either above or below the axis of theprime mover output shaft, as this enables the overall length of thepower train to be reduced without unduly increasing the overall width ofthe power train. The invention is particularly applicable forsit-astride type amphibious vehicles in which the engine compartment isgenerally thinner and taller than in other types of amphibious vehicles.

These and other features and advantages of the present invention willbecome apparent from the following detailed description of preferredembodiments which, taken in conjunction with the accompanying drawings,illustrate by way of example the principles of the invention.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention will now be described, by way of example only, withreference to the accompanying drawings, in which:

FIG. 1 is a schematic, partly sectioned, rear view of a “sit-astride”amphibious vehicle in accordance with the invention;

FIG. 2 is a schematic side elevation of a power train for use in thevehicle of FIG. 1;

FIG. 3 is a schematic plan view of the power train of FIG. 2;

FIGS. 4A to 4E are cross sectional views through a transfer gearbox ofthe power train of FIGS. 2 and 3, taken on line A-A of FIG. 3;

FIG. 5 is a partial, schematic view from the rear of the power train ofFIGS. 2 and 3, showing a modification to the drive line;

FIG. 6 is a view similar to that of FIG. 2, showing a further embodimentof a power train for use in an amphibious vehicle in accordance with theinvention; and

FIG. 7 is a view similar to that of FIGS. 2 and 6, showing a stillfurther embodiment of a power train for use in an amphibious vehicle inaccordance with the invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

With reference to FIG. 1, there is shown an amphibious vehicle 10. Thevehicle 10 is a “sit-astride” type of vehicle in which a user 12 sitsastride a saddle 14, in a manner similar to that of a motorcycle, jetski, quad bike or the like.

The vehicle 10 has two driven road wheels 16 at the rear. The roadwheels 16 are mounted such that they can be moved between a retractedposition in which they are elevated for use of the vehicle in water (asshown in FIG. 1) and a protracted position in which the wheels arealigned generally vertically, such that the main body 18 of the vehiclecan be supported clear of the ground on the wheels. Any suitable wheelretraction apparatus can be used to mount the rear wheels 16. Forexample, the rear wheels 16 may be mounted in accordance with thearrangement disclosed in International Patent Application No.PCT/NZ95/0013 published as WO 95/23074, the contents of which are herebyincorporated. Such a retractable wheel arrangement is particularlyhelpful where the vehicle is configured to plane over water.

For the avoidance of doubt, references to “vertical” or “vertically”throughout this specification, including the claims, should beunderstood as relating to a direction from top to bottom (or vice versa)of the vehicle when it is supported by its wheels or by its hull in anorientation conventional for locomotion; rather than a direction that isnecessarily orthogonal to the horizontal. The terms height, width andlength of the vehicle, should be construed accordingly.

The vehicle has longitudinal and transverse axes. The longitudinal axisextends substantially perpendicular to the vertical, through a pointsubstantially at the centre of the width and height of the vehicle, fromfront to back and vice versa. The transverse axis extends substantiallyperpendicular to the vertical, through a point substantially at thecentre of the length and height of the vehicle, from left to right andvice versa.

The vehicle 10 may also be provided with a further road wheel or wheels(not shown) towards the front of the vehicle. The front wheel or wheelsmay also be capable of being moved between retracted and protractedpositions and will be adapted to steer the vehicle on land in a mannerwell known in the art. In a preferred embodiment, the vehicle 10 has twofront wheels (not shown).

The main body 18 of the vehicle has bodywork 20 forming a compartment 22for housing at least part of a power train (indicated generally at 24 inFIG. 2) for the vehicle 10. As can be seen from FIG. 1, the compartment22 tends to be rather narrow and tall in order that the users legs canbe accommodated on either side.

A first embodiment of a power train 24 for use with the vehicle 10 shownin FIG. 1 can be seen in FIGS. 2 and 3. The power train 24 includes aprime mover 26, a transfer box 28, a bevel gear box 30, a speed changetransmission 32, a rear differential 34 and a marine propulsion unit 36.

The prime mover 26 will typically be an internal combustion engine butcould be any suitable type of prime mover, such as an electric motor ora hybrid engine and motor combination, for example.

As will be described in more detail below, the prime mover 26 providesdrive to both the rear wheels 16 of the vehicle and the marinepropulsion unit 36.

The prime mover 26 is located towards the front of the vehicle and hasan output shaft 38 that faces the rear of the vehicle for connectionwith the transfer box 28. Where the prime mover 26 is an engine, theoutput shaft may be the crankshaft of the engine. It will be noted thatthe axis of rotation of the prime mover output shaft 38 extends in alongitudinal direction of the vehicle. In the present embodiment, theaxis of rotation of the prime mover output shaft is inline with, or atleast parallel to, the longitudinal axis of the vehicle, as indicated atX in FIG. 3. However, it will be appreciated that this need not be thecase. The prime mover could be mounted so that the axis of rotation ofits output shaft is inclined to the longitudinal axis of vehicle.Indeed, the prime mover 26 could be mounted transversely so that theaxis of rotation of the prime mover output shaft 38 extends in a lateraldirection of the vehicle, as indicated at Z in FIG. 3.

A main drive shaft 40 is connected between the output shaft 38 of theprime mover and an input or primary shaft 42 of the transfer box. Wherethe prime mover is an engine, the main drive shaft 40 may be attached toa flywheel (not shown) mounted to the prime mover output shaft 38 in amanner well known in the art.

The transfer box 28 has two output shafts, a first land drive outputshaft 44 is connected to an input shaft 46 of the bevel gear box 30 by afurther drive shaft 48. A second output shaft 50 of the transfer boxcomprises a marine propulsion output shaft and is connected to themarine propulsion unit 36 by a yet further drive shaft 52.

The transfer box 28 is arranged to selectively couple drive from theprime mover 26 to the road wheels 16 and/or the marine propulsion unit36. The transfer box 28 also includes a reverse gear mechanism to enablethe direction of drive to the road wheels 16 to be reversed.

The detailed construction of the transfer box 28 can be seen in FIGS. 4Ato 4E. As already described, the output shaft 38 of the prime mover isconnected to the primary or input shaft 42 of the transfer box 28. Aninput gear 54 is mounted to and rotates with the primary shaft 42. Oneend of the primary shaft is supported for rotation in the casing 56 ofthe transfer box 28 whilst the other end is in rotational engagementwith the land drive output shaft 44. A first dog clutch 58 enables theprimary shaft 42 and the land drive output shaft 44 to be coupledtogether as shown in FIGS. 4B and 4D to transfer drive to the bevel gearbox 30, which is also shown schematically in FIG. 4A.

An intermediate gear 60 is mounted to a secondary shaft 62, which isitself mounted for rotation in the casing 56 of transfer box 28 ateither end. The intermediate gear 60 is in constant mesh with the inputgear 54 and is mounted for rotation with, or may be formed on, thesecondary shaft 62. A reverse input gear 64 is also mounted for rotationwith, or may be formed on, the secondary shaft 62. A reverse idler gear66 is in constant mesh with the reverse input gear 64 and is rotatablysupported on an idler shaft 68. A reverse land drive output gear 70 isassociated with a movable selector portion of the first dog clutch 58.The moveable selector portion of the first dog clutch 58 is slidablyengaged with the land drive output shaft 44 by means of splines 45. Asshown in FIG. 4C, the selector portion of the first dog clutch 58 can bemoved to bring the reverse land drive output gear 70 into mesh with thereverse idler gear 66 to enable drive to be transferred from the outputshaft 38 of the prime mover to the bevel gear box 30 but in a reversedirection.

A marine propulsion input gear 72 is mounted to a marine propulsioninput shaft 74 that is rotationally supported at one end in the transferbox casing 56. The other end of the marine propulsion input shaft 74rotationally engages with the marine propulsion output shaft 50. Asecond dog clutch 78 is provided to enable the marine propulsion inputshaft 74 and the marine propulsion output shaft 50 to be rotationallycoupled. With the second dog clutch 78 engaged, as shown in FIGS. 4D &4E, drive is transferred from the prime mover output shaft 38 via theinput gear 54, the intermediate gear 60, the marine propulsion inputgear 72 and the second dog clutch 78 to the marine propulsion outputshaft 50.

By appropriate engagement of the first and second dog clutches 58,78,and the reverse land drive output gear 70 it is possible toindependently and selectively transfer drive from the prime mover 26 tothe marine propulsion unit 36 and/or to the road wheels 16 and toreverse the direction of drive to the road wheels. FIG. 4A shows thetransfer box in neutral with both the first and second dog clutches 58,78 disengaged and no reverse gear selected. FIG. 4B, shows the transferbox with forward drive to the road wheels only (as indicated by arrow A)selected. In this case, the first dog clutch 58 is engaged and thesecond dog clutch 78 disengaged. FIG. 4C shows the moveable selectorportion of the first dog clutch 58 moved such that the reverse landdrive output gear 70 is engaged with the reverse idler gear 66 and withthe second dog clutch 78 disengaged. This arrangement provides reversedrive to the road wheels 16 only. FIG. 4D shows both dog clutches 58, 78engaged to provide drive to both the road wheels 16 and the marinepropulsion unit 36. Finally, FIG. 4E shows the second dog clutch 78engaged but the first dog clutch 58 disengaged and no reverse gearselected. Thus this arrangement would provide drive to the marinepropulsion unit 36 only.

It will be understood that the transfer box 28 may also include areduction gearbox type arrangement, having a ratio of 2:1 for example,in communication with the marine propulsion unit 36.

As already described, the land drive output shaft 44 of the transfer box28 is connected to an input shaft 46 of the bevel gear box 30 by a driveshaft 48. The bevel gear box 30 comprises at least a pair of bevel gears80, 82 arranged to turn the direction of the drive output from thetransfer box through 90 degrees. To this end, a first bevel gear 80 isrotationally fast with the bevel gear box input shaft 46 whilst thesecond bevel gear 82 is rotationally fast with an output shaft 84 of thebevel gearbox. The output shaft 84 of the bevel gear box projectsupwardly and has an axis of rotation Y that extends generally in avertical direction of the vehicle.

The speed change transmission 32 is positioned above the bevel gear box30 and has an input shaft 86 and an output shaft 88 both of which extendin a downward direction of the vehicle. In the present embodiment, theinput shaft 86 of the speed change transmission is positioned in linewith and is connected directly to the output shaft 84 of the bevel gearbox.

It should be noted that the axes of rotation of the input and outputshafts 86, 88 of the speed change transmission are orthogonal to a planethat extends both in a longitudinal and a lateral direction of thevehicle, i.e. a plane which includes both an axis (X in FIG. 3) runninglongitudinally of the vehicle and an axis (Z in FIG. 3) runningtransversely of the vehicle. In the present embodiment, the prime mover28 is positioned such that the axis of rotation of its output shaft 38is aligned generally horizontally and the axes of rotation of the inputand output shafts 86, 88 of the speed change transmission are orthogonalto a plane that includes the axis of rotation of the prime mover outputshaft 38 and extends transversely of the vehicle. However, it should beunderstood that the axes of rotation of the speed change transmissioninput and output shafts 86, 88 need not be orthogonal to the said planethat includes the axis of rotation of the prime mover output shaft.

Although the invention has been described with reference to the axis ofrotation of the speed change transmission input shaft 86 being angledgenerally orthogonal, i.e. at 90 degrees, to a longitudinal andtransverse (or lateral) plane of the vehicle, the axis of rotation ofthe input shaft 86 can also be arranged at other angles, such as mightbe required by the internal configuration of the vehicle: For example,the axis of rotation can be arranged at an angle of between 45 and 90degrees to the transverse and longitudinal plane of the vehicle, such asat 60 degrees to said plane. In any such case, the output shaft 88 ofthe speed transmission 32 can be arranged parallel to the input shaft 86or at any other required angle.

In the present embodiment, the speed change transmission 32 is acontinuously variable transmission (CVT). The detailed construction ofthe CVT transmission does not form part of the present invention andwill be known to those skilled in the art. However, in brief the CVTcomprises a primary pulley 90 associated with the input shaft 86, asecondary pulley 92 associated with the output shaft 88, and a drivebelt 94 extending between the two pulleys.

Whilst it is preferred that the speed change transmission is a CVT, thetransmission can be of any suitable type. For example, the speed changetransmission can be a manual, sequential manual or automated manualgearbox, it may also be an automatic or semi-automatic gearbox.

The output shaft 88 of the CVT is connected to the differential 34 whichdrives the two rear wheels 16 by means of drive shafts 96, 98. In thepresent embodiment the input to the differential is positioned in linewith the output shaft 88 of the transmission 32 enabling the outputshaft of the transmission 88 to be connected, either directly or bymeans of one or more intermediate shafts, to an input shaft of thedifferential. However, in some embodiments it may be necessary to offsetthe differential relative to the output shaft 88 of the transmission 32.In this case, drive between the transmission output shaft 88 and thedifferential can be interconnected using any suitable means. FIG. 5shows schematically an arrangement which allows the differential 34 tobe offset relative to the output shaft 88 of the transmission. In thismodification, a first drive sprocket 100 is mounted to the output shaft88 of the transmission and a second drive sprocket 102 is mounted to aninput shaft 104 of the differential and a drive chain 106 drivinglyinterconnects the first and second drive sprockets. This arrangementallows the input to the differential to be geared up or down ifrequired. A drive belt and pulleys may be used instead of a chain andsprockets.

As has already been described, the marine propulsion unit 36 isconnected to the marine propulsion output shaft 50 of the transfer boxby means of drive shaft 52 which may be an extension of, or be connectedto, an input shaft of the marine propulsion unit 36. Preferably themarine propulsion unit is a water jet but it could be of any suitabletype, such as a marine propeller. In certain embodiments, more than onemarine propulsion unit 36 can be provided, in which case drive from thetransfer box 28 can be split between the marine propulsion units 36 inany suitable manner as will be readily understood by those skilled inthe art.

FIG. 6 shows an alternative embodiment of a power train 24′ for use inan amphibious vehicle, such as that shown in FIG. 1. The same referencenumerals are used to designate similar components to those describedabove with reference to the power train 24 shown in FIGS. 2 and 3.

The power train 24′ is similar to the power train 24, except that thetransfer box 28 is omitted and the marine propulsion unit 36 is driventhrough the bevel gear box 30. This arrangement permits the maximumpossible power to be provided at the marine propulsion unit 36. At leastone additional bevel gear (not shown) may be provided in the bevel gearbox 30 to enable the drive for the marine propulsion 36 unit to be takenstraight through. Alternatively, input shaft 40 may be made integralwith output shaft 52.

Due to the omission of the transfer box, there is no provision in thedrive line of a reverse gear for reversing the direction of drive fromthe prime mover 26 to the road wheels 16. Where reverse drive of theroad wheels is required, this can be provided by means of a secondarypower unit 110, such as an electric motor or engine, that is arranged toprovide a reverse direction drive to the input of the differential 34.Advantageously, the secondary power unit 110 is an electric motor. Avehicle starter motor having a retractable Bendix drive is particularlysuitable.

It should be noted that the secondary power unit 110 is shownschematically in FIG. 6 and its position can be varied as required.

Although not shown in FIG. 6, a clutch or other means for disconnectingdrive from the prime mover 26 to the driven wheels 16 may also beprovided.

FIG. 7 shows a still further alternative embodiment of a power train 24″for use in an amphibious vehicle, such as that shown in FIG. 1. The samereference numerals are used to designate similar components to thosedescribed above with reference to the power train 10 shown in FIGS. 2and 3 and 6.

In this embodiment, the transfer box 28 is arranged on the output sideof a bevel gear box 30, in communication with the marine propulsion unit36. The transfer box 28 incorporates a reduction gearbox typearrangement (not illustrated) for selectively controlling the drive tothe marine propulsion unit 36.

Although not shown in FIG. 7, a clutch or other means for disconnectingdrive from the prime mover 26 to the driven wheels 16 may also beprovided.

It can be seen that the present invention provides a compact andversatile power train layout for an amphibious vehicle. By unusuallypositioning the speed change transmission such that its input shaftextends generally in a vertical direction of the vehicle, the speedchange transmission can be positioned above or below the axis of theoutput shaft of the prime mover. This enables the overall length of thepower train to be reduced and makes the power train particularlysuitable for use in sit-astride type amphibious vehicles. Positioningthe speed change transmission above the axis of the output shaft of theprime mover has the further advantage of raising the level of thetransmission reducing the risk of it getting wet during use of thevehicle on water.

Whereas the invention has been described in relation to what arepresently considered to be the most practical and preferred embodiments,it is to be understood that the invention is not limited to thedisclosed arrangements but rather is intended to cover variousmodifications and equivalent constructions included within the scope ofthe invention. For example, whilst the bevel gear box 30 and thetransfer box 28 are shown as separate components, it will be understoodthat the functions of the transfer box and the bevel gear box can beintegrated into a single unit. Furthermore, it will be appreciated thatwhere the speed change transmission is not a CVT, a clutch or fluidflywheel may be included in the power train to enable a smooth take upof drive from the prime mover 26. Furthermore, where four wheels areprovided, they may all be driven.

A reverse gear may be provided for the marine propulsion unit,particularly to assist in removal of weed or other foreign matter. Alsothe marine propulsion unit may be permanently driven whenever the primemover is operative; this may obviate the need for a flywheel.

Please note that as a further alternative arrangement (not illustrated),the transfer box 28 may be positioned upstream of bevel gear 30.

Whilst in the description above, the speed-change transmission islocated at a level vertically higher than the level of the output shaft40 and this is the preferred packaging, for some vehicles thespeed-change transmission could be at a level vertically lower than theoutput shaft 40, in which case the input shaft 86 of the speed-changetransmission would extend vertically downwards from the bevel gear box30 and the output shaft 88 would extend vertically upwards from thespeed change transmission.

While a particular form of the present invention has been illustratedand described, it will also be apparent to those skilled in the art thatvarious modifications can be made without departing from the spirit andthe scope of the present invention. Accordingly, it is not intended thatthe invention be limited except by the appended claims.

1. An amphibious vehicle comprising a power train, a body and a seatingposition where a driver of the vehicle sits externally to the body andastride thereof, the power train including a prime mover having anoutput shaft, a speed-change transmission having an input shaft, and amarine propulsion unit, the prime mover being arranged for driving themarine propulsion unit, and for driving at least one road wheel of thevehicle through the speed change transmission, wherein the speed changetransmission is mounted such that the axis of rotation of its inputshaft is angled relative to a plane including both transverse andlongitudinal axes of the vehicle.
 2. An amphibious vehicle as claimed inclaim 1, in which the axis of rotation of the speed change transmissioninput shaft is arranged generally orthogonal to the transverse andlongitudinal plane of the vehicle.
 3. An amphibious vehicle as claimedin claim 1, in which the axis of rotation of the speed changetransmission input shaft is arranged at an of angle between 45 and 90degrees to the transverse and longitudinal plane of the vehicle.
 4. Anamphibious vehicle as claimed in claims 1, in which the axis of rotationof the speed change transmission input shaft is arranged at an of angle60 degrees to the transverse and longitudinal plane of the vehicle. 5.An amphibious vehicle as claimed in claims 1, in which the axis ofrotation of the input shaft of the speed change transmission extendsgenerally in a vertical direction of the vehicle.
 6. An amphibiousvehicle as claimed in claims 1, in which the speed change transmissionis positioned such that its input shaft extends generally in a downwarddirection of the vehicle.
 7. An amphibious vehicle as claimed in claim1, in which said plane includes the axis of rotation of the prime moveroutput shaft.
 8. An amphibious vehicle as claimed in claim 7, in whichthe axis of rotation of the prime mover output shaft extends generallyhorizontally.
 9. An amphibious vehicle as claimed in claim 1, in whichthe axis of rotation of the prime mover output shaft extends in alongitudinal direction of the vehicle.
 10. An amphibious vehicle asclaimed in claim 1, in which the marine propulsion unit has an inputshaft and the marine propulsion unit is positioned such that an axis ofrotation of the marine propulsion unit input shaft extends in alongitudinal direction of the vehicle.
 11. An amphibious vehicle asclaimed in any previous claim 1, in which the speed change transmissionis a continuously variable transmission.
 12. An amphibious vehicle asclaimed in claim 1, in which the speed change transmission also includesan output shaft.
 13. An amphibious vehicle as claimed in claim 1 inwhich the axis of rotation of the speed change transmission output shaftis substantially parallel to the axis of rotation of the speed changetransmission input shaft.
 14. An amphibious vehicle as claimed in claim12, in which the speed change transmission output shaft extends in agenerally downward direction of the vehicle.
 15. An amphibious vehicleas claimed in claim 12, in which the power train further comprises adifferential through which at least two road wheels of the vehicle aredriven, the differential having an input shaft driven from the outputshaft of the speed change transmission, in which the axis of rotation ofthe input shaft is generally orthogonal to said plane.
 16. An amphibiousvehicle as claimed in claim 15, in which drive is transferred from theoutput shaft of the speed change transmission to the input shaft of thedifferential through a drive chain or belt.
 17. An amphibious vehicle asclaimed in claim 1, in which the power train further includes a transferbox for selectively coupling drive from the prime mover to the marinepropulsion means and/or the speed change transmission.
 18. An amphibiousvehicle as claimed in claim 17, in which the transfer box includes meansfor reversing the direction of rotation of drive to the speed changetransmission.
 19. An amphibious vehicle as claimed in claim 1, furtherincluding a pair of bevel gears in the drive line between the primemover and the speed change transmission for transmitting the drivethrough 90 degrees.
 20. An amphibious vehicle as claimed in claim 19, inwhich the bevel gears are contained in a bevel gear box, the bevel gearbox having an input shaft, a first output shaft for connection to aninput shaft of the speed change transmission, the first output shafthaving an axis of rotation orthogonal to the axis of rotation of theinput shaft, the bevel gear box having a second output shaft for drivingthe marine propulsion unit, the axis of rotation of the second outputshaft being in line with the axis of rotation of the input shaft.
 21. Anamphibious vehicle as claimed claim 1, in which drive from the primemover to the marine propulsion unit is permanently coupled.
 22. Anamphibious vehicle as claimed in claim 1, in which a secondary powerunit is provided to drive the at least one road wheel in a reversedirection of the vehicle.
 23. An amphibious vehicle as claimed in claim1, in which the vehicle is adapted such that a user sits astride thevehicle.
 24. An amphibious vehicle comprising a power train, the powertrain including a prime mover having an output shaft, a speed-changetransmission having an input shaft, and a marine propulsion unit, theprime mover being arranged to drive the marine propulsion unit and atleast one road wheel of the vehicle through the speed changetransmission, in which the speed change transmission is mounted in thevehicle such that its input shaft extends in a generally downwarddirection of the vehicle for connection with the drive line from theprime mover output shaft.
 25. An amphibious vehicle comprising a powertrain, a body and a seating position where a driver of the vehicle sitsexternally to the body and astride thereof, the power train including aprime mover having an output shaft, a speed-change transmission havingan input shaft, and a marine propulsion unit, the prime mover beingarranged for driving the marine propulsion unit and for driving at leastone road wheel of the vehicle through the speed change transmission,wherein the speed change transmission is mounted such that the axis ofrotation of its input shaft is angled relative to a plane including bothtransverse and longitudinal axes of the vehicle, further including apair of bevel gears in the drive line between the prime mover and thespeed change transmission for transmitting the drive through between 45and 90 degrees.
 26. An amphibious vehicle as claimed in claim 25, inwhich the bevel gears are contained in a bevel gear box, the bevel gearbox having an input shaft, a first output shaft for connection to aninput shaft of the speed change transmission and a second output shaftfor driving the marine propulsion unit.
 27. An amphibious vehiclecomprising a primer mover, a hull, road wheels, a sit-stride seat, amarine propulsion unit and a transmission for connecting the prime moverto drive at least one road wheel in a land mode of operation and forconnecting the prime mover to drive the marine propulsion unit in amarine mode of operation, wherein: the primer mover is located betweenan upper surface of the vehicle on which the sit-astride seat is locatedand a lower hull surface of the vehicle which is at least partlyimmersed in water during marine mode operation of the vehicle; theprimer mover has an output shaft; and the transmission relays to drivefrom the prime mover output shaft to the driven road wheel via a pathwhich extends upwardly from the prime mover towards the vehicle uppersurface and then downwardly to a connection of the transmission to thedriven road wheel.
 28. An amphibious vehicle as claimed in claim 27wherein the transmission comprises a speed-change transmission unitlocated nearer the vehicle upper surface than the prime mover.
 29. Anamphibious vehicle comprising a prime mover, a hull, road wheels, asit-astride seat, a marine propulsion unit and a transmission forconnecting the prime mover to drive at least one road wheel in a landmode of operation and for connecting the prime mover to drive the marinepropulsion unit in a marine mode of operation, wherein: the prime moveris located between an upper surface of the vehicle on which thesit-astride seat is located and a lower hull surface which is at leastpartly immersed in water during marine mode operation of the vehicle;the prime mover has an output shaft; and the transmission relays drivefrom the prime mover to the driven wheel via a path which extendsdownwardly from the prime mover towards the lower hull surface andupwardly to a connection of the transmission to the driven road wheel.30. An amphibious vehicle as claimed in claim 29, wherein thetransmission comprises a speed-change transmission unit located nearerthe lower hull surface of the vehicle than the prime mover.
 31. A powertrain configuration for use in an amphibious vehicle, comprising: aprime mover having an output shaft defining an axis; a marine propulsionunit drivable by said prime mover and positioned no higher than saidaxis; a speed-change transmission positioned wholly above said axis; andat least one road wheel drivable by said prime mover through saidspeed-change transmission.
 32. The power train configuration of claim31, wherein said speed-change transmission has an input shaft that isarranged at an angle of between 45 and 90 degrees relative to the outputshaft of said prime mover.
 33. The power train configuration of claim31, wherein said speed-change transmission has an output shaft andwherein said input shaft and output shaft of said speed-changetransmission are arranged in parallel and extend from the same side ofthe transmission.
 34. The power train configuration of claim 31, whereinsaid marine propulsion unit is positioned below said axis.
 35. The powertrain configuration of claim 31, wherein said marine propulsion unit hasan input shaft that is parallel to the output shaft of said prime mover.36. A sit-astride amphibious vehicle, comprising: a power train housinghaving a height that is greater than its width; a saddle disposed on topof said drive train housing for supporting a rider; a power train atleast partially housed within said housing, said power train including aprime mover with an output shaft defining a longitudinally extendingaxis and a speed-change transmission wholly disposed above said axis; atleast one road wheel drivable by said prime mover via said speed-changetransmission; and a marine propulsion unit, drivable by said prime moverand disposed no higher than said axis.
 37. The sit-astride amphibiousvehicle of claim 36, wherein said marine propulsion unit is disposedbelow said axis.
 38. The sit astride amphibious vehicle of claim 37,wherein said power train further includes a transfer box selectivelycoupling said prime mover to said marine propulsion unit.
 39. The sitastride amphibious vehicle of claim 36, wherein said speed-changetransmission includes an input shaft and an output shaft and whereinsaid input shaft is arranged at an angle of between 45 and 90 degreesrelative to said axis.
 40. The sit astride amphibious vehicle of claim39, wherein said input and output shafts of said transmission extendfrom a common side of such transmission.
 41. An amphibious vehicle powertrain, wherein a plane is defined by said vehicle's longitudinal axisand transverse axis, comprising: a prime mover having an output shaftparallel to said plane; a marine propulsion unit drivable by said primemover; a speed-change transmission having an input shaft arranged at anangle of between 45 and 90 degrees relative to said plane; and at leastone wheel drivable by said prime mover via said speed-changetransmission.
 42. The amphibious vehicle power train of claim 41,wherein said speed-change transmission is positioned above the outputshaft of said prime mover.
 43. The amphibious vehicle power train ofclaim 41, in which the output shaft of said prime mover lies in saidplane.
 44. The amphibious vehicle power train of claim 43, wherein saidspeed-change transmission is disposed above said plane.
 45. Theamphibious vehicle power train of claim 41, wherein saidspeed-transmission additionally includes an output shaft and whereinsaid input shaft and output shaft of said transmission extend from acommon side of said transmission.
 46. The amphibious vehicle power trainof claim 41, wherein said marine propulsion unit is disposed below saidplane.
 47. The amphibious vehicle power train of claim 41, furthercomprising a transfer box for selectively coupling said prime mover tosaid marine propulsion unit and/or said speed-change transmission. 48.The amphibious vehicle power train of claim 41, wherein said marinepropulsion unit is permanently coupled to said prime mover.
 49. Theamphibious vehicle power train of claim 41, wherein said speed-changetransmission comprises a CVT.
 50. The amphibious vehicle power train ofclaim 41, adapted for use within a sit-astride vehicle.